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The present invention relates to fluid pumps for elevating fluids from areas such as subterranean hydrocarbon bearing formations. More particularly, the present invention relates to traveling valves for use on sucker rod pumps. In particular, the present invention relates to such traveling valve having sliding shear seals therein.
Conventional oil and gas wells include a cased well bore with a tubing string extending down to the hydrocarbon bearing formation. The casing is perforated at the production level to permit the hydrocarbons to flow into the casing and the bottom of the tubing is generally open to permit the hydrocarbons to flow into the tubing and up to the surface. Oftentimes there is insufficient pressure in a formation to cause oil and other liquids to readily flow to the surface. It therefore becomes necessary to install some type of artificial lift system for pumping fluids to the surface.
One of the most common types of artificial lift systems is a sucker rod pump. This type of pump is positioned in the well at the level of the fluids to be removed and is mechanically driven by a series of rods connecting the pump to a pumping unit at the surface.
A sucker rod pump includes the simple combination of a cylinder or barrel with a piston or plunger and a suitable intake valve and a discharge valve. The intake valve is often referred to as a standing valve and the discharge valve is often referred to as a traveling valve.
Two of the more common types of sucker rod pumps are the tubing pump in which the pump barrel is attached directly to the tubing and is lowered to the bottom of the well as the tubing is run into the well. The plunger is attached to the bottom of the sucker rod and is positioned within the pump barrel. The intake valve is positioned at the bottom of the pump barrel and the traveling valve is positioned on the plunger. The second type of pump is often referred to as an insert pump and the entire assembly is attached to the bottom of the sucker rod. The barrel is held in place by a special seating nipple or other device positioned within the tubing. This type of pump has the advantage that it can more easily be removed for repair or replacement than a tubing pump. However, it suffers from the disadvantage of having a lower fluid capacity.
The operation of a sucker rod pump is relatively simple. The plunger reciprocates up and down in the barrel under the force of the sucker rod. During the upstroke, the traveling valve is closed and the fluid above the plunger is lifted to the surface by the plunger and sucker rod. At the same time, the standing valve is open allowing fluids to flow into and fill the now evacuated barrel. On the downstroke, the standing valve is closed thus trapping the fluids in the barrel. The traveling valve is opened allowing the compressed fluids to flow through the plunger so they can be lifted during the subsequent cycle.
While sucker rod pumps have been in use for decades and have proven to be economical and reliable, they still experience certain shortcomings and problems. Some of these problems are associated with valves which are generally of the ball-and-seat variety. This type of valve is opened and closed by pressure differentials across the valve.
One problem that is often encountered is referred to as gas lock. This occurs when there is a substantial amount of gas that flows into the pump with the liquid. Because of the high compressibility of the gas, insufficient pressure is generated during the downstroke of the pump to open the traveling valve against the hydrostatic pressure of the fluid in the production tubing. Accordingly, the pump can repeatedly cycle without any fluid being lifted to the surface.
Fluid pound is another problem that is often encountered. If the barrel is only partially filled with liquid the plunger forcefully encounters the liquid level part way through the downstroke thus causing severe stress to be placed on the pump. Pump off damage also occurs when the barrel is not completely filled with fluid. Damage occurs in the wall of the working barrel due to overheating of the pump which is caused by the absence of fluid to carry away the heat created by friction in the pump.
The problems associated with such traveling valves was addressed in U.S. Pat. No. 5,356,114, issued on Oct. 18, 1994, to the present inventor. This patent describes a mechanically operated traveling valve for use in a sucker rod pump. The valve included a cylindrical housing, a base positioned in the bottom of the housing which contains a first position of a sliding shear seal and a piston positioned within the housing of the base which contains a second position of the sliding shear seal. The valve is operable between open and closed positions by reciprocal actions on the piston which opens and closes the sliding shear seal.
Although this invention presented a very effective traveling valve which avoided the problems of the prior art, experiments involving this device showed that further problems were encountered. Most importantly, the enormous forces resulting between the surface on the piston which contacts the shoulder in the housing resulted in a fracturing of the shaft associated with the piston. Although various theories were developed as to why the shaft fractured as it did, it is believed that the two main reasons for such fracturing resulted from the flat surface-on-surface contact between the shoulder of the housing and the surface of the piston and the asymmetrical configuration of the cross-section of the piston in this area. Because of the asymmetrical cross-section, a bending moment occurred every time there was contact between the housing and the piston. Ultimately, after repeated use, this bending moment would tend to fracture this structure of the shaft. Whenever these fractures would occur, replacement of the traveling valve would be required. Such frequent replacements of the traveling valve resulted in enormous costs to the pump operator. Additionally, it was found that the shape of the piston in the area of the opening corresponding to the aperture in the housing would allow a limited amount of fluid flow through the housing, through the aperture and into the tubing string. However, the maximum area of fluid flow was restricted by the size of the diameter of the piston and the inner wall of the housing. As such, it would be desirable to maximize the area through which the fluid could flow into the tubing string.
It is an object of the present invention to provide a traveling valve which maximizes the operating life of the traveling valve.
It is another object of the present invention to provide a traveling valve which minimizes fractures to the shaft associated with the piston.
It is another object of the present invention to provide a traveling valve which maximizes fluid flow from the piston into the tubing string.
It is a further object of the present invention to provide a traveling valve which is relatively inexpensive, easy to manufacture, and easy to use.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a traveling valve for use in a sucker rod pump comprising a cylindrical housing having an interior passageway and a piston received within the interior passageway and slidable therein. The housing has its interior passageway extending from an upper end thereof to a bottom end thereof. The interior passageway has a tapered shoulder formed therein. The piston has a mechanically operated sliding shear seal positioned interior of the housing. This seal is operable between open and closed positions by the reciprocal action of the sucker rod. The piston has a surface thereon generally conforming to a shape of the tapered surface in the interior passageway.
In the present invention, the piston is movable between a first position and a second position. The seal is opened when the piston is in the first position. The seal is closed when the piston is in the second position. The surface of the piston is proximal the tapered shoulder of the housing when in the second position.
In the present invention, a tubing has the housing and the piston interior thereof. The tubing defines an annulus between an inner wall thereof and an exterior of said housing. The housing has an aperture formed therein. The piston is in fluid communication with the annulus through the aperture when the piston is in the first position. The housing has a first channel extending through a wall thereof so as to communicate between the annulus and the interior passageway adjacent a top of the tapered shoulder. The housing also has a second channel extending through a wall thereof so as to communicate between the annulus and the interior passageway in a location below the tapered shoulder.
In the preferred embodiment of the present invention, the tapered shoulder has a frustoconical configuration. The surface of the piston has a frustoconical shape matching the frustoconical configuration of the tapered shoulder.
The piston has a smaller diameter adjacent to the opening corresponding to the aperture of the housing when the piston is in the first position.
The present invention includes a base which is threadedly connected to the lower end of the housing. This base includes a first semi-cylindrical portion positioned within the housing and containing a portion of the sliding shear seal. The piston is positioned within the housing above the base with a shaft extending through the upper end of said housing. The piston includes a second semi-cylindrical portion which matingly engages a first semi-cylindrical portion of the base and contains a second portion of the sliding shear seal. A first passageway extends substantially through the length of the base with a first end in the bottom of the base forming the inlet to the traveling valve and a second end positioned in a longitudinal planar surface of the first semi-cylindrical portion forming an opening in the sliding shear seal. An aperture extends through the second cylindrical portion of the piston. This aperture is in alignment with the second end of the first passageway when the valve is in the opened position. A plate is positioned in a longitudinal planar surface of a first semi-cylindrical portion. This plate has an aperture formed therein corresponding to the first passageway. A disk positioned within a recess of a longitudinal planar surface of the semi-cylindrical portion of the piston. This disk is aligned such that it occludes the aperture in the plate when the valve of the closed position.